Case 1 : A 65-year-old man visited withfrequent urination and dysuria. Pyuria and bacteriuria were observed and prostate specific antigen (PSA) was elevated to 5.69 ng/ml. Prostate cancer and urinary tract infection were suspected. A antibiotics were administered and prostate magnetic resonance imaging (MRI) was performed. Massive prostate cancer was strongly suspected from the MRI findings and prostate needle biopsy was performed. The pathological examination revealed nonspecific granulomatous prostatitis. Case 2 : A 69-year-old man visited withfrequent urination. Urinalysis was normal and PSA was elevated to 4.52 ng/ml. Diffuse prostate cancer was suspected from the MRI findings and prostate needle biopsy was performed. Pathological findings were similar to those in case 1. Case 3 : A 61-year-old man presented withno urinary symptoms. Urinalysis was normal and PSA was elevated to 11.64 ng/ml. Medical history was renal pelvic cancer and bladder cancer. He had undergone a transurethral resection of the bladder tumor (TURBT) and intravesical Bacillus Calmette-Guérin (BCG) immunotherapy. Prostate cancer was suspected from the MRI findings and prostate needle biopsy was performed. Pathological findings were granulomatous prostatitis. In these three cases, the structure of these prostate capsules was preserved although extensive prostate cancer was suspected from the findings of MRI T2-weighted and diffusion weighted images. Although histopathologic examination is mandatory for differential diagnosis between granulomatous prostatitis and diffuse prostate cancer, prostate MRI may help to distinguish these diseases.